Catalytic bleaching with chlorites



Reissued Apr. 11, 1950 CATALYTIC BLEACHING WITH CHLORITES Robert M. Levy and James E. Brennan, Brevard, N. 0., assignors to Ecusta Paper Corporation, a corporation of Delaware N Drawing. Original No. 2,477,631, dated August 2, 1949, Serial No. 579,150, February 21, 1945. Application for reissue February 13, 1950,

Serial No. 144,025

7 Claims.

Our invention relates to the bleaching of cellulosic materials such as pulp for the manufacture of high quality paper, and textile fabrics, with chlorites of alkali metals or alkaline earth metals.

It is directed more particularly to thi type of 5 result can now be obtained by catalyzing the bleaching process and in which the action of the chlorite salt in aqueous solution with salts of the chlorites is catalyzed by water soluble salts of above mentioned metals. Typical examples of certain metals. satisfactory catalytic salts are cobalt chloride and One of the features of our catalytic process is cobalt nitrate. that it permits carrying out of the bleaching oper- The cellulosic materials to be bleached by the ation at substantially neutral or alkaline pH method of our invention include textiles, wood values. In accordance with our discovery the pulp and vegetable fiber pulp; typical examples catalytic salt permit efilcient bleaching with the being kraft wood pulp, [flex] flaw fiber pulp and chlorites at a pH range of about 5 to 8.5. Within cotton. The process is applicable generally to this range we have found a commercially advan- 5 pulps. produced by the conventional kraft, soda, tageous pH range of about 7 to 8. sulfite or neutral sulfite processes.

The use of these catalysts in accordance with Amounts of the chlorites and catalyst that may our invention markedly increases the activity of be used satisfactorily in accordance with our inthe chlorite bleaching compounds in neutral and vention vary widely. In general, it is not necesalkaline reaction solutions and enables the bleachsary to use more than about 0.5% of the catalyst ing to be carried out in equipment which is not salt based on the weight of the pulp to be acid-proof, such as for example, that normally bleached; and often-times this percentage of the used in the soda or kraft processes for producing catalyst may be as low as about 0.01%. In a paper p lp, typical case characteristic of our invention,

The chlorites that we may employ in the procsodium chlorite may be used as the bleaching ess of our invention include the [alkaline] alkali agent and cobalt nitrate used as the catalyzing metal chlorites, such as, sodium chlorite, and the agent for the chlorite. Under the p bleachalkaline earth chlorites, such as, calcium chlorite. ing conditions, and at neutral or alkaline pH The catalyst which we used to catalyze the values, up to pH 8.5, the cobalt nitrate will effect action of the chlorites and thereby render them decomposition of the sodium chlorite which effective bleaching agents i a neutral or effects bleaching of the cellulose without adverse line medium, include the water soluble salts of degradation, and e b in y be carried cobalt, nickel, [copper,] and an n The out in conventional, non-acid-proof equipment. catalytic effectiveness of these salts varies some a flllther F more Complete understanding what although they are in the same general of our nvention, the following illustrative but category from the standpoint of catalyzing the examples of the bleaching Opera; chlorite bleachin agent. The amounts required tmns are glvenfor effective use of these salts for catalyzing the EXAMPLE I chlorites are relatively very small as compared hl t krafl; pulp, in the amount of about with the amount of the chlorite compound itself. 40 grams, oven dry weight, was added to 940 In other words, the amounts of the catalytic salts of li containing Water, about 14 grams of required are in the Order Of characteristic sodium chlorite,.and about 0.09 grams of the cataamounts for catalyst, uch as f x p 001% lyst, cobalt nitrate. The latter was in the form to 0.5%. of a hexahydrate C0(N03)2.6H2O. The pH of the Although we do not wish to be limited to any 45 mixture was about 7.5. Suflicient water was used specific theory for explaining the effectiveness of to give the mixture a consistency of about 6% our invention, we believe that the chlorite is deand this fluid pulp suspension was held at a terncomposed by our catalyst to provide an adequate perature of about to C. for three hours. amount of chlorine dioxide, C102, which bleaches The pH value was maintained at about 7.5, by the cellulose. While it is relatively easy to obtain 50 additions of suitable alkali, such as caustic soda,

the chlorine dioxide gas from the chlorite salt, such as for example, sodium chlorite, NaClOz, by

Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue treatment with acid, it is much more difficult to eifect the decomposition and rapid formation of the C102 gas at the higher pH values, especially above a pH of 5. We have found that this desired as necessary. The formation of some insoluble cobalt pigment gives a slight discoloration, which is removed by a reducing compound, hydrosulfite. Following this treatment, the pulp was washed, and showed the following characteristics in comparison with the original pulp.

EXAMPLE II The results obtained in this example are as follows:

Original Bleached Pulp ulp Total available chlorine used. percent 3. Total nickel used do.. 0 0. 03 Brightness (G. E. meter)... 40 85 Viscosity (Tappi standard) 100 100 EXAMPLE HI The process given in Example I above was again carried out, in this case using materials similar to those in Example I, except for a change in the catalyst:

Chlorinated kraft pulp 60 Water 940 Sodium chlorite 1.4 Mn(SO4) .H2O 0.06

At the end of the bleaching process in this example, the dark colored manganese compound that was present .was removed by washing the bleached pulp with acidified water. The results Grams rites. It is when the pulp has reached the partially bleached stage and requires complete bleaching to a high brightness that it is most susceptible to degradation. In other words, the cellulose'is'more likely, to become degraded during the 'lattersta'ges of the bleaching operation, and in these stages we have found our catalytic -chlorite bleaching process to work most effectively.

Various other modifications and changes may 'be-made in the materials and process described 'hereinabove without departing from the scope of our invention, some of the novel features of which are defined in the appended claims.

Weclaim:

1.- In bleaching textiles, the improvement which comprises treating the textiles with an aqueous solution containing a chlorite of a metal of the class consisting of the [alkaline] alkali metals and the [alkali] alkaline earth metals, and a catalyst'for said chlorite comprising a relatively small amount of a water soluble salt of a metal of the class consisting of cobalt, nickel and manganese, and maintainin the pH during the bleaching operation at a value of about pH 5 to pH 8.5.

2. In bleaching vegetable fiber pulp, the improvement which comprises treating the vegetable fiber pulp with an aqueous solution containing a chlorite of a metal of the class consistin of the [alkaline] alkali metals and the [alkali] alkaline earth metals, and a catalyst for said chlorite comprising a relatively small amount of a water soluble salt of a metal of the class consisting of cobalt, nickel, and manganese, and maintaining the pH during the bleaching operation at a value of about pH 5 to pH 8.5.

3. In bleaching wood pulp, the improvement which comprises treating the wood pulp with an aqueous solution containing a chlorite of a metal of the class consistingof the [alkaline] alkali metals and the [alkali] alkaline earth metals,

; and a catalyst for said chlorite comprising a relaobtained in this example [as] are shown by the following values:

Original Bleached Pulp Pulp Available chlorine applied percent 0 3.0 Total manganese applied do,. 0 O. 03 Brightness (G. E. meter) c 41. 5 84.0 Viscosity (Tappi standard) H 38 35 The brightness and viscosity values in the above three examples showgood bleaching and high retention of viscosity which means that little or no degradation has resulted from the bleaching operation. The insoluble and somewhat discolored compounds that may be formed in the bleachin operations, such as the cobalt tively small amount'of a water soluble salt of a metal of the class consisting of cobalt, nickel, and manganese, and maintaining the pH during the bleaching operation at a value of about pH 5 to pH 8.5.

4. In bleaching cellulosic material, the improvement which comprises treating the cellulosic material with an aqueous solution containing a chlorite of a metal of the class consisting of the alkalimetals and the alkaline earth metals, and a catalyst for said chlorite comprising a relatively small amount of a water soluble salt of a metal of the class consisting of cobalt, nickel, and manganese, and maintaining the pH during the bleaching operation at a value of about pH 5 to pH 8.5.

5. In bleaching kraft pulp, the improvement which comprises treating the kraft pulp with an aqueous solution containing a chlorite of a metal of the class consisting of the alkali metals and the alkaline earth metals, and a catalyst for said chlorite comprising a relatively small amount of a water soluble salt of a metal of the class consisting of cobalt, nickel, and manganese,

and maintaining the pH during the bleaching operation at a value of about pH 5 to pH 8.5.

6. In bleaching flax pulp, the improvement which comprises treating the flax pulp with an aqueous solution containing a chlorite of a metal of the class consisting of the alkali metals and the alkaline earth metals, and a catalyst for said chlorite comprising a relatively small amount of same a water soluble salt of a metal of the class consisting of cobalt, nickel, and manganese, and 1 maintaining the pH during the bleaching operation at a value of about pH 5 to pH 8.5.

7. In bleaching soda pulp, the improvement which comprises treating the soda pulp with' ang aqueous solution containing a chlorite of a metali-f'i of the class consisting of the alkali metals and the alkaline earth metals, and a catalyst for said" chlorite comprising a relatively small amount of:

a water soluble salt of a metal of the class con-f sisting of cobalt, nickel, and manganese, and maintaining the pH during the bleaching operation at a value of about pH 5 to pH 8.5.

ROBERT M. LEVY. JAMES E. BRENNAN.

REFERENCES CITED The following references are of record in the file. of this patent and the original patent:

UNITED STATES PATENTS Number Name Date 321,452 Pond July 7, 1885 1,163,438 Muller Dec. 7, 191-5 1,777,751 Franz Oct. 7,1930" Number Name Date 1,904,190 Becher Apr.18, 1933 2,193,173 Jellinek Mar. 12, 1940 2,249,646 Bragg July 15, 1941 2,353,823 Hampel July 18, 1944 2,367,771 'Ha-mpel Jan. 23, 1945 FORETGN PATENTS Number Country Date 260,190 ,[Great Britain Oct. 28, 1926 311,435 Great Britain May 7, 1929 722,871 France Mar. 29, 1932 OTHER REFERENCES Hall, Monthly Review, Textile Colorist, January 1938, page 39. J

Taylor et al.,-Sodium Chlorite, Properties and Reactions, Industrial and Engineering Chemistry, July 1940, pages 899-903.

J. F. White etbil Chloritevs. HYpOchlorlte Bleaching, Technical Association of the Pulp and Paper Industry, September 1940, pages 159-164.

Taylor et al., Use of Sodium Chlorite in Bleaching," Tech. Assn Papers, 1940, Pa es 251-256, page 253 esp. pertinent. 

